Computer systems employ a number of storage means to store data. One of these storage means is a disk drive, which is also called a direct access storage device (DASD). A disk drive includes several disks that look similar to 45 RPM records used on a record player or compact disks used in a CD player. The disks are stacked on a spindle, much like several 45 RPM records awaiting to be played. In a disk drive, however, the disks are mounted on the spindle and spaced apart so that the separate disks do not touch each other.
The surface of each disk is uniform in appearance. Nevertheless, in actuality, each of the surfaces is divided into portions, called tracks, where data is stored. These tracks are arranged in concentric circles like rings in a tree. Compact disks have tracks as do the disks in a disk drive. The tracks in either the disk drive or the compact disk essentially replace the grooves in a 45 RPM record. Each track in a disk drive is further subdivided into sectors, which are just sections of one of the concentric tracks.
Disk are made of a variety of materials, such as metal, plastic, or glass. In a plastic disk, such as those used as CD's, a laser stores and retrieves the data. In a metal disk, an electrical magnet, commonly known as a transducer, stores and retrieves the data.
In order to store data on a magnetic disk, the disk surface is magnetized using a small ceramic block, commonly called a slider, that contains a magnetic transducer, called a write head. More specifically, the slider containing the write head is flown at a height of a few millionths of an inch from the disk surface, and the head is energized to various states causing the track below to be magnetized to represent the data.
To retrieve data stored on a magnetic disk, the slider containing a read head is flown over the disk. This time the magnetized portions of the track induce a current in the read head. By analyzing the current output from the read head, the computer system can reconstruct and use the data stored on the magnetic disk. Although some disk drives use a separate read and write head, most current disk drives use a transducer that acts as both the read and write head.
Like a record, both sides of a disk are generally used to store data or other information necessary for the operation of the disk drive. Since the disks are held in a stack and are spaced apart from one another, both the top and the bottom surface of each disk in the stack of disks have their own read and write heads. This is analogous to a stereo that could play both sides of a record at the same time, each side having its own stylus.
There are two types of disk drives, those with rotary actuators and those with linear actuators. Rotary actuators have an actuator arm, which is analogous to a record player tone arm. Like a tone arm, the actuator arm rotates so that the slider containing the read and write heads is moved to locations over various tracks on the disk. In this way, the read and write heads can be used to magnetize a track on the surface of the disk in a pattern representing the data or used to detect the magnetized pattern on a track. For example, the needed data may be stored on two different tracks on one particular disk, so to read the magnetic representations of data, the actuator arm is rotated from one track to another track. This invention is concerned with rotary actuator disk drives.
A linear actuator has a similar actuator arm, however, repositioning is accomplished through linear instead of rotational movement.
The actuator arm of a disk drive has a slider affixed at the end, which holds the read and write heads. Also affixed to the slider are rails. When the disk rotates, air is dragged between the rails and the disk surface causing pressure, which forces the head away from the disk. The head is thus said to fly over the rotating disk. The fly height is the thickness of the air lubrication film, i.e., the distance between the disk surface and the head.
Thus, a rail is an air bearing surface (ABS) that forms and maintains a self-pressurizing air lubrication film between the head and the disk recording surface. This film eliminates the friction and resulting wear that would occur if the head and disk were in mechanical contact during disk rotation.
Previous ABS designs consisted primarily of a two-rail tapered configuration known as taper-flat sliders. The two-rail taper-flat configurations typically had two or more flat rails each having a tapered forward edge. The rails were elongated and the tapered edge faced toward the direction of rotation of the disk surface. These designs worked well in linear actuator disk drives when the flow of air between the disk and the slider was primarily uni-directional along the length of the rails. In other words, these designs worked well when the slider was positioned with respect to the disk such that the flow of air was viscously dragged under the slider from the front of the slider to the back along a longitudinal axis parallel to the rails. The taper-flat design concept dates back to large diameter file designs having relatively low access rates which use linear actuators.
Today's disk drive files are much different from the large diameter disk drives which used linear actuators. Current files are much smaller and feature high-speed access of data. Currently, disk drives have disks with 5.25", 3.50", 2.50" or 1.80" diameters and feature rotary actuators to achieve high-speed access rates. Mainly due to the use of rotary actuators, the air flow under the slider is no longer substantially uni-directional, but varies widely in angle with respect to the longitudinal axis of the slider. In addition, high speed seek motion of the actuator during accessing causes angular flow between the head and disk. Therefore, in modern rotary actuator disk drives, the flow of air can no longer be considered as moving from the front to the back of the slider, or even at small deviations from front to back.
The angle of the air flow with respect to the longitudinal axis of the slider is called the skew angle. If the actuator arm is positioned such that the air flow strikes the outside, or rim, edge of the slider, then the skew angle is said to be positive. If the actuator arm is positioned such that the air flow strikes the inside, or hub, edge of the slider, then the skew angle is said to be negative. The taper-flat design is susceptible to a severe reduction of fly height at high positive or negative skew angles and large access speeds because the taper-flat slider was designed for linear actuators rather than for rotary actuators.
Also, the skew angle of the air flow can cause the slider to roll such that the flying height is not uniform under all the rails. Roll of a slider is analogous to the roll of an airplane when it banks into a turn; one wing goes up while the other wing goes down. In a disk drive, a positive roll occurs when the rim rail rolls away from the disk surface, while a negative roll occurs when the rim rail rolls toward the disk surface.
The fly height of a slider in a disk drive is a critical parameter that must be controlled. An increase in fly height can cause a decrease in signal amplitude and a decrease in the signal to noise ratio, thus increasing the error rate. A degradation in fly height can increase the likelihood that the head will come into contact with the disk surface, causing accelerated wear on both the head and disk surfaces, causing reduced reliability, and even causing failure of the disk drive. A severe contact with the disk surface which causes a failure is called a crash and results in the inability to recover data.
Control of the roll of the slider is also important. When roll lowers a corner of the slider, the likelihood is increased that the head will come into contact with the disk surface. Roll that raises one corner of the slider can increase the distance of the read and write heads from the disk surface, causing data errors in the same manner that increasing the fly height of the slider causes data errors. This effect of roll is exacerbated in sliders where the read and write heads are mounted on the corner of the slider that is raised.
A recent patent that allegedly lessons the problems caused by skew angle and roll is U.S. Pat. No. 4,870,519 issued to White on Sep. 26, 1989. White modified the basic taper-flat slider design by adding a longitudinal step to the slider edge. The White invention has numerous disadvantages, including additional manufacturing processes to make the steps. The steps also introduce additional fly height sensitivities, and the steps provide the potential of contamination from debris accumulation.
The present invention is a different solution to the same problems of degraded fly height without the disadvantages of the White patent. The present invention has no stepped or convex edges, so it avoids additional processes, fly height sensitivities, and the potential for contamination from debris accumulation. The present invention also can be manufactured with a single etching mask operation, while the stepped or convex edges of White would require multiple mask operations. It would also be possible to form the slider by other methods such as by grinding the slider.